Prolonging internal power supply life in a mobile communication device

ABSTRACT

A method of communicating between a mobile communication device including a power supply, and a base station. The mobile device has first and second alternative communication modes, the first communication mode having higher quality of service and higher power consumption than the second communication mode. The second communication mode is adopted in response to a characteristic of the mobile device power supply indicative of a reduced reserve of power in the power supply, and a state indication is transmitted from the mobile device to the base station. The base station can respond to the state indication from the mobile device by modifying a communication characteristic of the base station with the mobile device, whereby to tend to compensate for the mobile device switching between the first and second communication modes.

FIELD OF THE INVENTION

This invention relates to prolonging internal power supply life in amobile communication device. The invention is especially, but notexclusively, applicable to reducing mobile device power consumption in acellular network.

BACKGROUND OF THE INVENTION

Mobile communication devices, such as portable telephones in a cellularnetwork or two-way radio devices include an internal power supply,usually a rechargeable battery. Reducing power consumption of suchdevices is a constant preoccupation in order to maximise the life of thepower supply. However, there is often a trade-off between quality ofservice, especially quality of communication, and power consumption,leading to compromises both in design features and operating parameters.

In cellular communication networks and other radio communicationsystems, the communication channel from the transmitter to the receiveris subject to noise and interference from multipath transmissions causedby scattering and transmission of the same data by more than onetransmitter. One way of reducing the effect of noise and interference isspatial diversity, in which the receiver and/or the transmitter have aplurality of antennas and the received signals are received in separatereceiver chains and combined so as to reinforce the wanted signal and/ortransmitted signals containing the same data are processed in separatetransmit chains. The use of separate receiver or transmitter chainsincreases power consumption but provides improved quality of service.

U.S. Pat. Nos. 7,072,628 and 6,724,828 disclose cellular communicationnetworks using spatial diversity, in which the use of receive diversityin a mobile device can be disabled in response to parameters indicativeof good quality communication conditions for the relevant communicationchannel, so as to reduce power consumption when spatial diversity givesreduced benefits in terms of quality of communication.

Quality of service of a mobile device deteriorates rapidly when theinternal power supply is nearly exhausted, especially if it suppliespower at a reduced voltage and/or current, for example. An object of thepresent invention is to improve the compromise between quality ofservice, and power consumption in these conditions.

SUMMARY OF THE INVENTION

The present invention provides a method of communication, a mobiledevice and a base station as described in the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a cellular telephone system which mayoperate by a method of communication in accordance with one embodimentof the invention, given by way of example,

FIG. 2 is a block schematic diagram of a receiver module for a mobiledevice in the system of FIG. 1 in accordance with an embodiment of theinvention, given by way of example,

FIG. 3 is a flow chart of operation of the receiver module of FIG. 2 ina mobile device by a method of communication in accordance with anembodiment of the invention, given by way of example,

FIG. 4 is a block schematic diagram of a transmitter module for a mobiledevice in the system of FIG. 1 in accordance with an embodiment of theinvention, given by way of example,

FIG. 5 is a block schematic diagram of a receiver module for a basestation in the system of FIG. 1 in accordance with an embodiment of theinvention, given by way of example,

FIG. 6 is a block schematic diagram of a transmitter module for a basestation in the system of FIG. 1 in accordance with an embodiment of theinvention, given by way of example,

FIG. 7 is a flow chart of operation of the transmitter module of FIG. 4in a mobile device by a method of communication in accordance withanother embodiment of the invention, given by way of example,

FIG. 8 is a flow chart of operation of the receiver module of FIG. 5 ina base station by a method of communication in accordance with yetanother embodiment of the invention, given by way of example, the basestation responding to operation of the transmitter module in a mobiledevice in accordance with FIG. 7

FIG. 9 is a flow chart of operation of the transmitter module of FIG. 6in a base station by a method of communication in accordance with yetanother embodiment of the invention, given by way of example, the basestation responding to operation of the receiver module in a mobiledevice in accordance with FIG. 3, and

FIG. 10 is a flow chart of operation of a mobile device and a basestation by a method of communication in accordance with yet anotherembodiment of the invention, given by way of example, the mobile deviceand base station including receiver modules as in FIGS. 2 and 5 andtransmitter modules as in FIGS. 4 and 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention may operate in accordance withvarious communication standards. Examples of such standards, includingcode division multiple access (‘CDMA’), are the UMTS standard of theInternational Telecommunication Union (ITU), the 3^(rd) generationpartnership project (‘3GPP’) under the auspices of the EuropeanTelecommunications Standards Institute (ETSI), the CDMA2000 standard ofthe Telecommunications Industry Association of USA and the WCDMAair-interface specification.

FIG. 1 shows a general diagram of a cellular telephone network 100 towhich embodiments of the present invention may be applied. The networkincludes a public switched telephone land line network 102, to which areconnected a first base station 104 having a transmit/receive antennaarray 106 and a second base station 108 having a transmit/receiveantenna array 110. Although two base stations are shown, it will beappreciated that in practice more will be provided, whose coveragedefine respective cell areas within the geographic extent of the network100. Mobile devices, such as handsets, 112, 116 and 120 provided withrespective antenna arrays 114, 118 and 122 can move within the network,communicating with the base stations. The communication will typicallybe multipath, involving multiple reflections and/or partial shading. Ata given moment, a given mobile device may communicate with a single basestation, as is shown for mobile devices 116 and 120 with base station104, or simultaneously with more than one base station, as is shown formobile device 112 with base stations 104 and 108. In the latter case,the base stations 104 and 108 may transmit identical data to the mobiledevice 112 and may receive identical data from the mobile device 112.Data is transmitted between the base stations and the mobile devicesboth in content channels and in control channels, sometimes known aspilot channels, which may transmit information about channelidentification, propagation conditions, timing, modulation and encodinginformation and the like.

FIG. 2 is a diagram of a receiver module 200 in accordance with anembodiment of the invention for use in a mobile device in a network ofthe kind illustrated in FIG. 1 for processing and demodulating thesignal received.

The receiver module 200 for a mobile device, such as 112, 116 or 120 ofFIG. 1, includes two antenna elements 202 and 204 and respective RFreceiver chains 206 and 208. It will be appreciated that more than twoantenna elements and RF chains may be provided. Samples of basebandsignals received by the RF chains 206 and 208 are supplied to a samplestore 210, which holds the samples temporarily. The samples, togetherwith the outputs of the RF chains 206 and 208 are supplied to amultiplexer 212. The output of the multiplexer 212 is supplied to asearcher 214 and to a plurality of demodulation and de-spreading fingerelements 216, whose outputs are combined by a combiner 218 and suppliedto a decoder 220, such as a turbo decoder. The output of the searcher214 is supplied to a control unit 222, which controls operation of theRF chains 206 and 208, the multiplexer 212, the searcher 214 and thefinger elements 216, the control unit also responding to the output ofthe decoder 220. The searcher 214 responds to received pilot signalswhich identify communication channels and timing and the demodulationand de-spreading is performed using the complex conjugate of the PNsequence and assigned Walsh function, for example.

Such a receiver 200 normally functions to improve the quality ofreception by exploiting the spatial diversity offered by the differentantenna elements 202 and 204 and associated RF receiver chains 206 and208, under the control of the control unit 222 and various suitabletechniques for exploiting the spatial diversity are available. However,the receiver module 200 of this embodiment of the invention for use in amobile device with a battery (or other internal power supply) 224 alsoincludes a battery voltage sensor 226. The battery 224 supplies power tothe whole of the receiver 200 for the mobile device, including the RFchains 206, 208, and a reduced power consumption of the RF chains 206,208 slows the depletion of the energy reserve of the battery 224. Thecontrol unit 222 is responsive to a value of the battery voltage lessthan a threshold at which loss of reception is becoming imminent toadopt a mode of communication having smaller power consumption than thenormal mode and accept a correspondingly reduced quality of service ofthe receiver, in particular a reduced quality of communication. It willbe appreciated that reducing power consumption during the period whenbattery voltage is low postpones total loss of the communication linkand gives the user more time to communicate until he is able to rechargethe power supply. Generally speaking, reduction of the quality ofservice is undesirable, but nonetheless it is preferable in thesecircumstances to rapid total loss of communication.

More specifically, in the embodiment of the invention shown in FIG. 2,when a low battery condition is detected, the control unit 222 acts todisable one or more of the RF chains such as 206, 208, keeping one RFchain operational at minimum. This disables partially or totally supportin the receiver for spatial diversity reception. In this embodiment ofthe invention, the control unit 222 also causes the transmitter of themobile device to send over the uplink to the base stations a stateindication indicative of the change of communication mode adopted by themobile device.

An example of a method of operation of the embodiment of the inventionshown in FIG. 2 is illustrated in FIG. 3. In this embodiment of theinvention, the mobile device has two alternative modes of communication,a first one of which has a higher quality of service and higher powerconsumption than the other. Normally the first mode of communication isutilised. However, the other communication mode offering a reduction inpower consumption is selected by the control unit in response to sensingof a low battery condition. In this embodiment of the invention, thereduction of power consumption is obtained by a reduction of support forreceive spatial diversity.

More specifically, FIG. 3 is a flow-chart of the method, which begins at300. A decision is taken at 302 whether the mobile device receiver isoperating with full receive diversity support, with both the RF chains206 and 208 activated. If so, a check is made at 304, whether thebattery sensor 226 indicates a low battery condition, by sensing whetherthe battery voltage is lower than the threshold Vth. If the battery isnot low, the receiver is left with full receive diversity support andthe control loop returns to the beginning. If the battery 224 is low,the control unit 222 disables receive diversity support at 306 partiallyor, where there are only two RF chains 206 and 208, totally by disablingone of the chains and economising its power consumption by switching offthat RF chain's power supply. A state indication indicative of reducedreceive diversity support is produced by the control unit 222 at 308,and the mobile device transmits this state indication to the basestation, terminating the control cycle at 310.

If the decision taken at 302 is that the mobile device receiver is notoperating with full receive diversity support and only one of the RFchains 206 and 208 is enabled, a check is made at 312 whether thebattery sensor 226 indicates a low battery condition, by sensing whetherthe battery voltage is lower than the threshold Vth. If the battery 224is low, the receiver is left without full receive diversity support andthe control loop returns to the beginning. If the battery 224 is notlow, the control unit 222 activates receive diversity support again at314 by switching back on the disabled RF chain's power supply andaccepting the increased power consumption. The state indicationindicative of reduced receive diversity support is de-asserted by thecontrol unit 222, and the mobile device transmits the correspondingstate indication to the base station at 308, terminating the controlloop at 310.

In another embodiment of the invention, other characteristics of theinternal power supply indicative of a reduced reserve of energy aresensed, such as battery current, for example.

FIG. 4 shows a transmitter module 400 in accordance with an embodimentof the invention for use in a mobile device in a network of the kindillustrated in FIG. 1 for processing and modulating the signal to betransmitted with capability for transmit diversity. It will beappreciated that a mobile device having receive diversity capabilitydoes not necessarily have transmit diversity capability also, althoughthis may be desirable.

The transmitter shown in FIG. 4 comprises a modulator 402, whichreceives data whose content is to be transmitted. A spreader andamplifier 404 processes the modulated signal. A pilot signal isgenerated by a generator 406 and added to the spread and amplifiedsignal in an adder 408. A transmit controller 410 selects the datatransmission rate and the transmit power by controlling the modulator402 and processor 404. The combined signal from the adder 408 istransmitted by a plurality of RF chains, in this example two chains 412and 414, which comprise respective RF power amplifiers and may alsocomprise delay elements (not shown) and feed respective antenna elements416 and 418, which may also be used for reception. In this embodiment ofa transmitter with controllable transmit diversity in a mobile device,the transmit controller 410 also controls the activation anddeactivation of transmit spatial diversity. In the case of a mobilecommunication device with receive diversity control as in FIGS. 2 and 3for example, whether with transmit diversity control as in FIG. 4 orwithout, the generator 406 may include in the transmissions to the basestation diversity state indications of the activation and deactivationof receive spatial diversity and/or of transmit spatial diversity. Thebattery 224 supplies power to the whole of the transmitter 400 for themobile device, including the RF chains 412, 414, so that a reduced powerconsumption of the RF chains 412, 414 slows the depletion of the energyreserve of the battery 224.

In the embodiment of the invention shown in FIG. 4, anothercommunication mode offering a reduction in power consumption for amobile communication device is reduced transmit spatial diversityselected by the transmit controller 410 in response to sensing of a lowbattery condition instead of, or as well as, reduction of receivespatial diversity support. In this way, a cell phone or other mobilecommunication device offers spatial diversity in the receiver and/ortransmitter but also permits a graceful degradation of performance inresponse to low battery conditions. Although FIG. 4 shows a transmitterwhere reduction of power consumption is obtained by a reduction oftransmit spatial diversity, in other embodiments of mobile devices inaccordance with the present invention, other alternative modes ofcommunication are used offering a reduction of power consumption in lowbattery conditions.

FIG. 5 is a diagram of a receiver module 500 in accordance with anembodiment of the invention for use in a base station in a network ofthe kind illustrated in FIG. 1 for processing and demodulating thesignal received.

The receiver module 500 for a base station, such as 104 or 108 of FIG.1, includes two antenna elements 502 and 504 and respective RF receiverchains 506 and 508. It will be appreciated that more than two antennaelements and RF chains may be provided. Samples of baseband signalsreceived by the RF chains 506 and 508 are supplied to a sample store510, which holds the samples temporarily. The samples, together with theoutputs of the RF chains 506 and 508 are supplied to a multiplexer 512.The output of the multiplexer 512 is supplied to a searcher 514 and to aplurality of demodulation and de-spreading finger elements 516, whoseoutputs are combined by a combiner 518 and supplied to a decoder 520,such as a turbo decoder. The output of the searcher 514 is supplied to acontrol unit 522, which controls operation of the RF chains 506 and 508,the multiplexer 512, the searcher 514 and the finger elements 516, thecontrol unit also responding to the output of the decoder 520. Thesearcher 514 responds to received pilot signals which identifycommunication channels and timing and the demodulation and de-spreadingis performed using the complex conjugate of the PN sequence and assignedWalsh function, for example.

The receiver 500 normally treats the channels used by different mobiledevices according to similar criteria, which may vary according to thedistance of the mobile device from the receiver 500, for example.However, the receiver 500 also has the possibility to devote additionalresources to enhance reception of a signal from a particular mobiledevice, under the control of the control unit 522. More particularly,the control unit 522 is responsive to a state indication transmitted bythe mobile device to the base station. In this embodiment of theinvention, the state indication is an indication of the transmit modestatus of the mobile device. In another embodiment of the invention, thestate indication is representative of a low battery condition of themobile device.

FIG. 6 shows a transmitter module 600 in accordance with an embodimentof the invention for use in a base station in a network of the kindillustrated in FIG. 1 for processing and modulating the signal to betransmitted with capability for transmit diversity. It will beappreciated that a base station having receive diversity capability doesnot necessarily have transmit diversity capability also, although thismay be desirable.

The transmitter shown in FIG. 6 comprises a modulator 602, whichreceives data whose content is to be transmitted. A spreader andamplifier 604 processes the modulated signal. A pilot signal isgenerated by a generator 606 and added to the spread and amplifiedsignal in an adder 608. A transmit controller 610 selects the datatransmission rate and the transmit power by controlling the modulator602 and processor 604. The combined signal from the adder 608 istransmitted by a plurality of RF chains, of which two chains 612 and 614are shown in FIG. 6 although more may be provided, and which compriserespective RF power amplifiers and may also comprise delay elements (notshown), the chains 612 and 614 feeding respective antenna elements 616and 618, which may also be used for reception.

The transmitter 600 in the base station normally treats the channelsused by different mobile devices according to similar criteria, whichmay vary according to the distance of the mobile device from thetransmitter 600, for example. However, the transmitter 600 also has thepossibility to devote additional resources to enhance transmission of asignal to a particular mobile device, under the control of thecontroller 610, in particular as a function of state indications sent bythe mobile device and received by the base station receiver. In thisembodiment of the invention, the controller responds to an indicationthat the mobile device is operating with reduced receive diversity, toincrease transmit power from the base station for the channel of thatmobile device for example. Alternatively, or additionally, thecontroller 610 may respond to a state indication transmitted by themobile device and representative of a low battery condition of themobile device.

The controller 610 may also select intended operating modes for themobile device transmitter and receiver, in particular reduced powerconsumption operating modes for the mobile device, with reduced qualityof service and send to the generator 606 corresponding command signalsfor inclusion in the pilot signals transmitted to the mobile device,such as commands for the activation and deactivation of receive spatialdiversity and/or of transmit spatial diversity at the mobile device.

An example of a method of operation of the mobile device transmitterembodiment of the invention shown in FIG. 4 is illustrated in FIG. 7. Inthis method of communication, the mobile device has two alternativemodes of communication, a first one of which has a higher quality ofservice and higher power consumption than the other. Normally the firstmode of communication is utilised. However, the other communication modeoffering a reduction in power consumption is selected by the controlunit in response to sensing of a low battery condition. In thisembodiment of the invention, the reduction of power consumption isobtained by disabling transmit spatial diversity. The reduction of powerconsumption of the mobile device by adopting a reduced quality oftransmission service may be additional to, or alternative to, adopting areduced quality of reception service, such as shown in FIG. 4.

More specifically, FIG. 7 is a flow-chart of the method, which begins at700. A check is made at 702 whether the controller 410 is selectingnormal transmit quality of service, in this case full transmitdiversity, by activating both the RF chains 412 and 414. If so, a checkis made at 704 whether the battery sensor 226 indicates a low batterycondition, by sensing whether the battery voltage is lower than thethreshold Vth. If the battery is not low, the transmitter is left withfull transmit quality of service and the control loop returns to thebeginning. If the battery 224 is low, the controller 410 reducestransmit quality of service at 706, in this case by disabling transmitdiversity support partially or, where there are only two RF chains 412and 414, totally by disabling one of the chains and economising itspower consumption by switching off that RF chain's power supply. A stateindication indicative of reduced transmit quality of service is producedby the controller 410 at 708, and the mobile device transmits this stateindication to the base station, terminating the control loop at 710.

If the decision taken at 702 is that the controller 410 is not selectingfull transmit quality of service, in this case is disabling one of theRF chains 412 and 414 and accepting reduced transmit diversity, a checkis made at 712 whether the battery sensor 226 indicates a low batterycondition, by sensing whether the battery voltage is lower than thethreshold Vth. If the battery 224 is low, the transmitter is leftwithout full transmit quality of service and the control loop returns tothe beginning. If the battery 224 is not low, the controller 410activates normal transmit quality of service again at 714 by switchingback on the disabled RF chain's power supply and accepting the increasedpower consumption. The state indication indicative of reduced transmitquality of service is de-asserted by the controller 410, and the mobiledevice transmits the corresponding state indication to the base stationat 708, terminating the control loop at 710.

Transmission from the mobile station to the base station of a stateindication enables the base station to react. If the decision to changethe mobile device's communication mode is taken unilaterally in themobile device, transmission of a state indication signalling the changedcommunication mode, or even simply signalling the low battery condition,enables the base station to change its own communication parameters andtend to compensate for reduced quality of service at the mobile device.For example, if the mobile device signals a disablement of receivediversity, the base station may increase its transmit power to tend tocompensate. If the mobile device signals a disablement of transmitdiversity, the base station may increase its receiver gain to tend tocompensate or allocate more receive resources such as receive diversitypaths or digital signal processor MIPS to that mobile device.

An example of the base station's reaction to a unilateral change of themobile device's transmit mode is illustrated in FIG. 8, in which thecontrol loop of the base station receive controller begins at 800. Inthis case, a state indication of the reduced power transmit mode at themobile device is transmitted over the uplink to the base station withoutany direct indication of the mobile device's low battery condition. Acheck is made at 802 whether the state indication from the mobile devicecorresponds to reduced power transmit mode. If so, a decision is takenat 804 whether the base station control unit 522 is selecting enhanceduplink path gain, with increased diversity and receive amplifier gaindevoted to that mobile device, for example. If that is the case, thebase station is left with high uplink path gain and the control loopreturns to the beginning. If normal uplink path gain is currentlyselected, the base station switches to high uplink path gain at 806 andthe control loop ends at 808.

If the result of the check at 802 was that the state indication from themobile device corresponds to normal power transmit mode, for examplewith full diversity, a decision is taken at 810 whether the base stationcontroller 522 is selecting high uplink path gain. If normal uplink pathgain is selected, the base station is left with unchanged uplink pathgain and the control loop returns to the beginning. If high uplink pathgain is currently selected, the base station switches to normal uplinkpath gain at 812 and the control loop ends at 808.

An example of the base station's reaction to a unilateral change of themobile device's receive mode is illustrated in FIG. 9, in which thecontrol loop of the base station transmit controller begins at 900. Inthis case, a state indication of the receive diversity mode at themobile device is transmitted over the uplink to the base station withoutany direct indication of the mobile device's low battery condition. Thisstate indication may be in the form of a signal asserted when the mobiledevice receive diversity is de-activated and de-asserted when the mobiledevice receive diversity is activated. A decision is made at 902 whetherthe state indication corresponds to full receive diversity at the mobiledevice. If not, a check is made at 904 whether the base stationcontroller 610 is applying enhanced transmit power to the signals forthat mobile device. If not, the base station transmit power for thatchannel is increased at 906 and the control loop ends at 908. If thebase station controller is applying transmit power at 904, the basestation transmitter is left with increased transmit power and thecontrol loop returns to the beginning.

If the check at 902 corresponds to reduced receive diversity at themobile device, a check is made at 910 whether the base stationcontroller is applying enhanced transmit power to the signals for thatmobile device. If it is, the base station transmit power for thatchannel is reduced back to normal at 912 and the control loop ends at908. If the base station controller is already applying normal transmitpower at 910, the base station transmitter is left with normal transmitpower and the control loop returns to the beginning.

The state indication transmitted by the mobile device may, at leastinitially, be an indication that the energy reserve of the battery 224is low, as sensed by the battery voltage being lower than a fixed orprogrammable threshold, for example. In this case, in other embodimentsof the present invention, instead of the mobile device changingcommunication mode unilaterally, the base station reacts by sending tothe mobile device an instruction to change to a reduced powerconsumption mode selected by the base station. This enables the basestation to to coordinate more complex changes to to the communicationmodes, including its own communication mode. Examples of such complexchanges are adopting at both ends a more power efficient modulationscheme, such as Gaussian Minimum Shift Keying (GMSK) instead of EnhancedData Rates for GSM Evolution (EDGE), or higher performance transportprotocols such as High-Speed Uplink Packet Access and High-SpeedDownlink Packet Access which can reduce the amplifier linearityrequirements at the mobile device and allow reduced current drain. Inaddition, the change of communication mode at the mobile device may beconfirmed back subsequently to the base station, which is desirable insome circumstances to avoid incompatibility, for example if theinstruction to the mobile station is lost.

FIG. 10 illustrates an embodiment of the present invention thatfunctions in this manner. The operation begins in the mobile device at1000 and a decision is made at 1002 whether the mobile device batteryvoltage is below a threshold indicating low energy reserve. If thebattery indication is low, at 1004 the mobile device transmits over theuplink to the base station a low battery state indication and waits fora command from the base station, checking the reception of the commandat 1006. If the battery state indication was not low at 1002, theoperation passes directly to the check at 1006.

When a command to adopt a selected QOS and power consumption mode isreceived at 1006, the mobile device makes a check at 1008 whether itscurrent operating mode corresponds to the command from the base station.If it does, at 1010 the mobile device sends to the base station a stateindication of its current operating mode and the cycle ends at 1012. Ifthe mobile device operating mode does not correspond to the base stationcommand at 1008, the mobile device adopts the power consumption modecorresponding to the base station command at 1014 and at 1010 sends tothe base station a state indication of its new operating mode and thecycle ends at 1012. Normally, if the battery state indication was low at1002, the base station command at 1014 will correspond to a reducedpower consumption mode. The state indication sent to the base stationmay be a signal that is de-asserted when the mobile device is operatingin normal mode. The reduced power consumption mode may be a reducedquality of communication by reduced receive diversity and/or reducedtransmit diversity. In other embodiments of the invention, the reducedpower consumption mode involves a more power efficient modulation schemeor higher performance transport protocols, as described above.

The operation of the base station in this embodiment of the inventionbegins at 1100. A check is made at 1102 whether a state indicationindicating a low battery condition is received from the mobile device.If not, the base station checks at 1104 whether it is operating inenhanced quality of service mode for that mobile device's channel, bydevoting additional receive and/or transmit resources to that channel,for example. If not, the control loop returns to the beginning. If thebase station is operating in enhanced mode at 1104, it selects normalcommunication mode for that channel at 1106, sends a correspondingindication to the mobile device at 1108, instructing the mobile deviceto adopt normal communication mode, and waits to receive a response fromthe mobile device at 1110 indicating the mobile device's currentoperating mode. The base station then checks at 1112 whether the mobiledevice operating mode state indication corresponds to the selected modeand if so the base station adopts the selected mode at 1114 and thecontrol loop ends at 1116. If the mobile device operating mode stateindication does not correspond to the selected mode, the base stationreverts to stage 1108 and re-transmits the indication of the selectedmode to the mobile device.

If at stage 1102 the state indication from the mobile device indicates alow battery condition, the base station checks at 1118 whether it isoperating in enhanced quality of service mode for that mobile device'schannel. If it is, the control loop passes directly to stage 1108. If itis not, the base station selects its enhanced quality of service at 1120and proceeds to stage 1108, sending to the mobile device a command toadopt a corresponding power saving mode.

Instead of a command to adopt a selected QOS and power consumption mode,in another embodiment of the invention the command transmitted from thebase station to the mobile station is a command to adopt a reduced powerconsumption mode when selected by the base station, and which isde-asserted otherwise. In yet another embodiment of the invention thecommand transmitted from the base station to the mobile station is acommand to change communication mode from the current mode to a definedalternative mode.

The invention claimed is:
 1. A mobile communication device forcommunicating with a base station and having first and secondalternative communication modes, said first communication mode havinghigher quality of service and higher power consumption than said secondcommunication mode, and said device comprising: a power supply; whereinsaid mobile device is responsive to a characteristic of said powersupply indicative of a reduced reserve of energy in said power supply toselect said second communication mode and transmit to said base stationa state indication identifying existence of a low energy condition ofsaid power supply, said state indication to cause said base station torespond by allocating more resources to reception of signals transmittedby said mobile device operating in said second communication mode thanin said first communication mode wherein said mobile communicationdevice is arranged to express in said second communication mode acharacteristic selected from a group consisting of: a differentmodulation scheme in said second communication mode from said firstcommunication mode for communication with said base station; a differenttransport protocol in said second communication mode from said firstcommunication mode for communication with said base station; more basestation receive diversity resources allocated by said base station toreception of said signals transmitted by said mobile communicationdevice in said second communication mode from said first communicationmode; and increased transmit power of base station signals to saidmobile communication device in said second communication mode relativeto said transmit power of base station signals to said mobilecommunication device in said first communication mode.
 2. A mobilecommunication device as claimed in claim 1, wherein said stateindication transmitted to said base station is arranged to identify acommunication mode adopted by said mobile device.
 3. A mobilecommunication device as claimed in claim 1, responsive to a signal fromsaid base station to adopt said second communication mode aftertransmitting to said base station said indication identifying existenceof a low energy condition of said internal power supply.
 4. A mobilecommunication device as claimed in claim 1, wherein said characteristicindicative of a reduced reserve of energy in said power supply is apower supply voltage less than a threshold voltage (Vth).
 5. A mobilecommunication device as claimed in claim 1, wherein said firstcommunication mode of said mobile device includes spatial receivediversity support, which is arranged to be reduced or disabled in saidsecond communication mode of said mobile device.
 6. A mobilecommunication device as claimed in claim 1, wherein said mobile deviceis arranged to communicate with said base station employing EnhancedData Rates for GSM Evolution (EDGE) in said first communication mode andcommunicate employing Gaussian Minimum Shift Keying in said secondcommunication mode.
 7. A mobile communication device as claimed in claim1, wherein said mobile device is arranged to transmit at lower power insaid second communication mode than in said first communication mode. 8.The method of claim 1, wherein said characteristic comprises saiddifferent modulation scheme in said second communication mode from saidfirst communication mode for communication with said base station. 9.The method of claim 1, wherein said characteristic comprises saiddifferent transport protocol in said second communication mode from saidfirst communication mode for communication with said base station. 10.The method of claim 1, wherein said characteristic comprises said morebase station receive diversity resources allocated by said base stationto reception of said signals transmitted by said mobile communicationdevice in said second communication mode from said first communicationmode.
 11. The method of claim 1, wherein said characteristic comprisessaid increased transmit power of base station signals to said mobilecommunication device in said second communication mode relative to saidtransmit power of base station signals to said mobile communicationdevice in said first communication mode.
 12. A method of communicatingbetween a mobile communication device and a base station, said mobiledevice having first and second alternative communication modes, saidfirst communication mode having higher quality of service and higherpower consumption than said second communication mode, and said mobiledevice including a power supply, said method comprising: selecting saidsecond communication mode in response to a characteristic of said mobiledevice power supply indicative of a reduced reserve of power in saidpower supply; transmitting from said mobile device to said base stationa state indication identifying existence of a low energy condition ofsaid power supply; and responding at said base station to said stateindication by allocating more resources to reception of signalstransmitted by the mobile device operating in said second communicationmode than in said first communication mode wherein said respondingcomprises an operation selected from a group consisting of: employing adifferent modulation scheme in said second communication mode from saidfirst communication mode for communication with said mobile device;employing a different transport protocol in said second communicationmode from said first communication mode for communication with saidmobile device; allocating more base station receive diversity resourcesto reception of said signals transmitted by said mobile communicationdevice in said second communication mode from said first communicationmode; and increasing transmit power of base station signals to saidmobile communication device in said second communication mode relativeto transmit power of said base station signals to said mobilecommunication device in said first communication mode.
 13. A method ofcommunicating as claimed in claim 12, wherein a state indicationtransmitted from said mobile device to said base station also identifiesa communication mode adopted by said mobile device.
 14. A method ofcommunicating as claimed in claim 12, wherein said mobile deviceresponds to a signal from said base station to adopt said secondcommunication mode after transmitting to said base station said stateindication identifying existence of a low energy condition of saidinternal power supply.
 15. A method of communicating as claimed in claim12, wherein said characteristic indicative of a reduced reserve ofenergy in said power supply is a power supply voltage less than athreshold voltage (Vth).
 16. A method of communicating as claimed inclaim 12, wherein said base station responds to said state indicationfrom said mobile device by modifying a communication characteristic ofsaid base station with said mobile device, whereby to tend to compensatefor said mobile device switching between said first and secondcommunication modes.
 17. A method of communicating as claimed in claim16, wherein said base station and said mobile device communicateemploying Enhanced Data Rates for GSM Evolution (EDGE) in said firstcommunication mode and communicate employing Gaussian Minimum ShiftKeying in said second communication mode.
 18. A method of communicatingas claimed in claim 16, wherein said base station and said mobile devicecommunicate employing High-Speed Uplink Packet Access—HSUPA—with asmaller number of HSUPA channels in said second communication mode thanin said first communication mode.
 19. A method of communicating asclaimed in claim 12, wherein said first communication mode of saidmobile device includes spatial receive diversity support, which isdisabled in said second communication mode of said mobile device.
 20. Amethod of communicating as claimed in claim 19, wherein said basestation responds to said state indication from said mobile device byincreasing transmit power of signals to said mobile device if it isoperating in said second communication mode relative to transmit powerof signals if said mobile device is operating in said firstcommunication mode, whereby to tend to compensate for said mobile deviceswitching between said first and second communication modes.
 21. A basestation for communicating with a mobile communication device andincluding means responsive to said state indication for controlling theresponses of the base station as specified in claim
 12. 22. The methodof claim 12, wherein said operation comprises said employing saiddifferent modulation scheme in said second communication mode from saidfirst communication mode for communication with said mobile device. 23.The method of claim 12, wherein said operation comprises said employingsaid different transport protocol in said second communication mode fromsaid first communication mode for communication with said mobile device.24. The method of claim 12, wherein said operation comprises saidallocating more base station receive diversity resources to reception ofsaid signals transmitted by said mobile communication device in saidsecond communication mode from said first communication mode.
 25. Themethod of claim 12, wherein said operation comprises said increasingtransmit power of said base station signals to said mobile communicationdevice in said second communication mode relative to transmit power ofsaid base station signals to said mobile communication device in saidfirst communication mode.
 26. A method of communicating between a mobilecommunication device and a base station, said mobile device having firstand second alternative communication modes, said first communicationmode having higher quality of service and higher power consumption thansaid second communication mode, and said mobile device including a powersupply, said method comprising: monitoring at said mobile device suasponte a characteristic of said power supply indicative of a reducedreserve of power in said power supply; selecting said secondcommunication mode in response to said characteristic of said mobiledevice power supply indicative of a reduced reserve of power in saidpower supply; and transmitting from said mobile device to said basestation a state indication identifying existence of a low energycondition of said power supply said base station responding to saidstate indication with a response selected from a group consisting of:employing a different modulation scheme in said second communicationmode from said first communication mode for communication with saidmobile device; employing a different transport protocol in said secondcommunication mode from said first communication mode for communicationwith said mobile device; increasing base station receive diversitysupport to reception of said signals transmitted by said mobilecommunication device in said second communication mode from said firstcommunication mode; and increasing transmit power of base stationsignals to said mobile communication device in said second communicationmode relative to transmit power of base station signals to said mobilecommunication device in said first communication mode.
 27. The method ofclaim 26, wherein said response comprises said employing a differentmodulation scheme in said second communication mode from said firstcommunication mode for communication with said mobile device.
 28. Themethod of claim 26, wherein said response comprises said employing adifferent transport protocol in said second communication mode from saidfirst communication mode for communication with said mobile device. 29.The method of claim 26, wherein said response comprises said increasingbase station receive diversity support to reception of said signalstransmitted by said mobile communication device in said secondcommunication mode from said first communication mode.
 30. The method ofclaim 26, wherein said response comprises said increasing transmit powerof base station signals to said mobile communication device in saidsecond communication mode relative to transmit power of base stationsignals to said mobile communication device in said first communicationmode.